Covalently modification of DNA by diolepoxides metabolically formed from polycyclic aromatic hydrocarbons(PAHs) such as benzo[a]pyrene (BaP) provides a mechanism for the genotoxicity, mutagenicity, and carcinogenicity of PAHs. We continue toinvestigate the solution structures of DNA containing different stereoisomers of benzo[a]pyrene diol epoxides (BaP DE) that are covalently bound to dA. We have investigated a 12-mer DNA duplex containing the base sequence for the major dA mutational hot spot in the HPRT gene when Chinese hamster V79 cells are given low doses of highly carcinogenic (+)-(R,S,S,R-BP DE2 enantiomer. 2Dchemical exchange-only experiments indicate dynamic behavior near the intercalation site especially at the 10R adducted dA, such that this base interconverts between the normal anti conformation and a less populated syn conformation. The existence of conformational flexibility around adducts may be related to the occurrence of multiple mutagenic outcomes resulting from a single DE adduct. We also investigated the effect of hydrophobicity at the saturated benzo-ring of BaP DE on solution structures of two undecadeoxynucleotide duplexes, d(CGGTCA*CGAGG).(CCTCGTGACCG),with a thymidine base opposite 10R adducts derived from transaddition of deoxyadenosine N6-amino group of a centrally located deoxyadenosine (dA6) to(-)-(7S,8R,9R,10S)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydro benzo[a]pyrene (BaP DE2) and it's(-)-(9R,10S)-7,8-dihydro-9,10-epoxy analogue (BaP H4; lacking hydroxyl groups at C7 and C8 positions of BaP DE2). The results show that these two adducts exhibit remarkable resemblance bothin NMR data and computational structures. Despite the remarkable conformational similarity, subtle local structural difference is noticed for the dA6-dT17 base pair between these two adducts. These results indicate that the 7,8-diols which are metabolically produced during diol epoxide formation play relatively insignificant role in the gross conformation of the adduct. The subtle local structural difference at the adduct site of these adducts, however, may account for the variation in their mutational profile.